1. Field of the Invention
The present invention relates to a method for improving the contour of rolled material. Specifically, the present invention relates to a method for increasing the rolled material length within a rolling schedule or for achieving a more free, customized configuration of the rolling schedule, without regard to the varying width of the strips. The present invention may be achieved by axially shifting at least one of the work rolls of at least one rolling stand in hot rolling or cold rolling plants. The axial shifting may occur as a function of a quality criterion, which may be in the form of a mathematical function, which is optimized.
2. Discussion of Background Information
During rolling, in particular during hot rolling, the contour of the work rolls may be subjected to continuous changes within a rolling schedule. The rolling schedule includes the rolling processes between two work roll changes. The work rolls wear significantly at the edge of the rolling stock. The resulting changes in the contour may be compensated for by axially shifting the work rolls.
EP 0276 743 B1, for example, discloses a type of cyclical shifting, wherein a specific shifting path of the work rolls is set so that the wearing of the rolls and the thermal roll crown is distributed more uniformly in the axial direction. However, this method is inadequate to achieve a sufficiently smooth roll contour.
EP 0 219 844 B1 discloses a method for setting the profile of rolling stock by axially adjusting the positions of an upper and lower work roll in opposite directions. In this case, the profile of each work roll is determined during rolling. From this profile, the gap between the work rolls is determined as a function of the magnitude of the relative adjustment of the roll positions. Thus, later, it is possible to determine which magnitude of the adjustment of the roll positions may produce a smoother configuration in the axial direction for the gap inside the contact region between the workpiece and work rolls. This document discloses the calculation of only the subsequent shift position.
It may be gathered from the article titled "Schedule-Free Rolling Strategies Based on Contour Control for Flexible Hot Strip Mill Concepts" by K. Eckelsbach, G. Kneppe, D. Rosenthal, H. Wolters, SMS Schloemann-Siemag AG, Dusseldorf and Hilchenbach/Germany, ISIDM '97 Conference Proceedings, pages 163-171, that, in the case of contour monitoring in hot strip rolling mills, use is made of a process model from which suitable shift positions of the work rolls are derived. Anomalies thereby occurring in the contours, admittedly of the hot rolled strip, are described by a quality criterion which can be treated mathematically. As shown on page 168 of this article, the roll shift positions are determined from one strip to the next in each case.
EP 0 618 020 A1 discloses a method for achieving a prescribed target contour of a rolled strip, it being possible to use various control elements to achieve this target contour when using at least two rolling stands of a hot strip train or when using at least two roll passes in a reversing stand. If a strip contour deviates from the target contour, the mechanical control elements are used to produce a minimum deviation of the calculated strip shape from the target contour. In this case, the optimization of the strip contour is disclosed for one strip.
DE 37 12 043 A1 discloses a control device wherein the current strip profile is analyzed, inter alia, to subsequently carry out an optimum axial shift of axially shiftable rolls to achieve an unstressed hot rolled strip. DE 40 40 360 A1 discloses a control concept for each strip currently being worked, certain model equations and control elements being adapted based on measured variables.
With respect to these last two publications, a plurality of strips are never taken into account in advance.
DE 44 21 005 A1 describes a pass schedule optimization by using process models which supply the number of the passes, the rolling forces during the individual passes, etc. However, determining axial shift positions of the work rolls is not part of the pass schedule optimization.